It is regularly available, and some manufacturers even provide kits. This is one of the things that made me curious.

I have never repacked a car or bike muffler, have never noticed an issue or change, have never seen hot spots on the muffler indicating a problem inside, etc. Thus I am curious if this is a real world issue, only for the fussy, or limited to a racer's concern where sustained high RPM full throttle produces a difference environment and is hard on mufflers.

I *think* the factory mufflers on my ST-1300 are designed with various baffles that split and route exhaust and sound in different internal paths such that there is no packing in the first place. They also have integrated cats, which in and of themselves result in quite a bit of silencing. They definetly are sealed, and there is no way to open them up anyway...